Systemic juvenile idiopathic arthritis (SJIA) is a rheumatic condition characterized by arthritis, quotidian fever, evanescent rash, and sometimes other types of systemic inflammation. SJIA is currently thought to be a multigenic, autoinflammatory disease, but the molecular details of its pathogenesis are still unknown. A striking feature of SJIA is its association with macrophage activation syndrome (MAS), a complication that can be fatal. This clinical aspect, together with data from immunophenotypic studies of SJIA, points to the monocyte lineage as being important in disease pathogenesis. Activated monocytes express components of the inflammasome, a multiprotein complex that senses infectious or noxious stimuli and activates caspase-1, leading to maturation and secretion of IL-1beta and IL-18 and sometimes to host cell death IL-1beta and IL-18 have been implicated in SJIA. Based on our preliminary data, we hypothesize that monocytes from SJIA patients harbor a defect in the inflammasome pathway. The objective of this R21 proposal is to discover host pathways and genes that influence IL- 1beta maturation and release by monocytes and to test these as candidate disease associated factors. In Aim 1, we will take a candidate approach to characterize possible defects in SJIA monocytes by measuring known molecular events related to IL-1beta secretion in cells from SJIA patients compared to cells from age-matched immunologically normal children. Specifically, we will measure cytokine release, activation of caspase-1, caspase-1 regulated cell death, levels of expression of Rab 39a, the purinergic receptor P2X7R, and the pore-forming protein, pannexin-1. Findings will be followed up with sequencing of associated candidate genes in 35 SJIA patients. In Aim 2, we will take a less biased approach and conduct a forward genetic screen to identify host factors that influence IL-1beta secretion in normal cells. This screen will likely provide additional candidate factors potentially affecting IL-1beta biology in SJIA. Our results will delineate molecular components regulating IL-1 processing and secretion and, ultimately, could result in new and innovative approaches to the prevention and treatment of SJIA and other autoinflammatory diseases. PUBLIC HEALTH RELEVANCE: Systemic juvenile idiopathic arthritis (sJIA) is a chronic rheumatic condition in children characterized by remitting fever, transient rash, and relapsing arthritis. Although sJIA represents only 10-20% of the total cases of chronic inflammatory arthritis in children (JIA), it accounts for more than 2/3 of JIA mortality, due to complications o this disease and its treatment. The cause of sJIA is unknown, but recent evidence strongly suggests that a driving force is excessive activity of an endogenous inflammatory mediator called IL-1. This conclusion is based on the efficacy of anti-IL-1 therapy in a large subset of sJI patients, especially if this treatment approach is instituted early. We are interested in elucidatig the basis of uncontrolled IL-1 activity in sJIA. The Mellins laboratory has been studying the immune cells found in the blood of children with sJIA and has found evidence for abnormal regulation of IL-1 secretion in these cells. The Monack laboratory has been studying the basic cellular mechanisms that control IL-1 secretion in immune cells. While certain aspects of IL-1 control have been uncovered, such as the importance of a subcellular structure known as the inflammasome, it is clear that more molecular events remain to be discovered. Using modern genetic and biochemical approaches, our laboratories will work to identify the molecular steps involved in production and secretion of active IL-1 from immune cells. We then will go on to determine at which step(s) the immune cells from sJIA patients are abnormal. This project will contribute important new knowledge on the fundamental processes involved in inflammation and will shed light on the mechanism of disease in a chronic, sometimes fatal illness of children, sJIA. The project also has the potential to identify approaches to treatments for sJIA and other inflammatory diseases where IL-1 plays a pathogenic role.